1. Field of the Invention
The present invention is directed to the provision for hot runners for an injection molding machine.
2. Description of the Prior Art
Injection molding machines generally comprise a horizontal mold unit and a horizontal injection unit, or a vertical mold unit and a vertical injection unit. Some injection molding machines comprise a horizontal mold unit and a vertical injection unit, or a reverse combination.
With such machines, the runner within the mold is designed to have a minimized length to assure a smooth flow of the material. However, since the mold itself must be provided with a hot runner portion, there is a need to use a machine including the mold and hot runner portion and which is designed specifically in conformity with the shape of the desired molding. This entails an increased equipment cost and a reduced mold cooling efficiency.
To overcome the above problem, Published Unexamined Japanese Patent Application SHO No. 50-66558 discloses an injection molding machine comprising a mold and an L-shaped hot runner portion separate from the mold. A nozzle and a cylinder head constituting the hot runner portion are upwardly or downwardly movable for the nozzle to come into contact with the mold to supply a material to the mold cavity.
With this conventional arrangement, the cylinder head is connected directly to a plasticizing cylinder, which is pivoted at its base portion to effect the upward or downward movement for nozzle touching. Accordingly when the horizontal part of the hot runner portion thermally expands, the arrangement is unable to accommodate the expansion properly, permitting the nozzle to touch the mold at an improper position to result in a leak of material or produce a thermal stress.